Modern inspection, defect review and metrology tools use one or more charges particle beams in order to inspect, analyze and measure features or defects. The resolution of these systems is responsive to various parameters including the focus error, astigmatism and the like. Modern systems are also required to inspect, review or measure samples with an increased throughput. High throughput systems requires fast focus error detection methods.
As the size of features and defects gets smaller there is a need to provide an efficient method for determining focus errors.